Servers by jDrones

CUAV C-RTK 9P Test

(cuavle) #1


The C-RTK 9P is a high-precision RTK module designed by CUAV based on the Ublox F9P module.
I happened to see Andrew Tridgell’s test article on F9P by chance. I wanted to test C-RTK 9P., With the help of Andrew Tridgell, I learned how to use log and MAVProxy for data analysis. Thanks to @Andrew Tridgell !

My test data:

Test Equipment

  • C-RTK 9P 2(One as Base and one as Rover)
  • CUAV V5 plus FC 1
  • Multi-frequency antenna 2
  • PC 1
    Test locationt

This is the place I tested, and there are buildings around it.
base station

I used a C-RTK 9P as the base station. It completed the base station configuration in one minute. According to my experience, its satellite signal receiving capability is much higher than that of the M8P module.

Rover test

RTK fix

It easily enters the RTK fix state and keeps it. I tested the M8P module multiple times in the same place, and it was very difficult to get into the RTK fix, it just kept the RTK float state. So I think it is better than the M8P.

Horizontal accuracy

As you can see from the two figures above:
The longitude fluctuates between 113.6016711~113.6016714, and the latitude fluctuates between 22.7531004~22.7531006, and the position accuracy is about 2cm.

Alt accuracy

Alt accuracy is 2CM

Speed accuracy

This is the horizontal speed accuracy。

GPS Reported Accuracy

GPS Reported Accuracy affects the mixing ratio of GPS in the EKF, which affects the flight of the drone.

This is my test data, the horizontal report accuracy is 2CM, and the Alt report accuracy is 1CM. It is better than the test data of Andrew Tridgell , because it is always in the RTK fix state.

Speed Accuracy

This is speed report accuracy, it may not be as good as other data.

Above is all my test data, more professional test articles, please see Andrew Tridgell’s article:Comparing a uBlox F9P with a M8P with RTK.

for C-RTK 9P:http://ardupilot.org/copter/docs/common-cuav-c-rtk-9p-gps.html
CUAV docs:http://doc.cuav.net/gps/c-rtk/en/

2 Likes
(Kikislater) #2

1000 bucks ! Quite expensive for f9p module …

(ZED-PV ) #3

Considering you need 2 to run this system, I agree with the comment above. It’s quite expensive.

Another option is a Polaris Alpha RTK set.

2 will set you back about 400USD and there is an antenna that is UAV compatible/reasonably sized.
Though you can use any antenna with the same specs or better. It has UART output just as the CUAV 9P.

But I have to say the CUAV 9P does have more constellations and frequencies, also double the update rate at 20hz over 10hz of the Alpha.

If they cut the price in half then I’m sure price to feature wise it would beat the Alpha set.

(hans bert) #4

why dont u use the piksi multi ?
two frequency, around 500$ per module.

very usefull.

(Kikislater) #5

Cheaper way is to get the true value of F9P : simplertk2b or csgshop. 500$ is still expensive and out of topic, discussion is about ublox f9p not about closed and proprietary devices …

(Reflection 3D Technology) #6

Too expensive, we will consider if it is 300$

(cuavle) #7

It is doing a 50% discount and this is just the retail price. CUAV is taking on expensive cross-border trade costs, and we prefer to find partners who will get more affordable prices.

(curt carroll) #8

When you compare reported elevations do these accuracy numbers match your findings.?

(tridge) #9

My preferred way of running RTK is to use a NTRIP server, which means you don’t need a base station which reduces cost a lot.
I will do an article at some stage on how to find NTRIP servers. There are free NTRIP servers in a lot of places around the world.

3 Likes
(Kikislater) #10

It depends … Some country (eg: in Africa or Small Island) don’t have or if you are far more than hundred (optimist) kilometers from your ntrip caster, it still needs a base !

And now watch the price, just laughing : what a shame ! Just go away from them … CSG Shop, SimpleRTK2B or Drotek sold them cheaper and on a more robust platform that poor Aliexpress …

(curt carroll) #11

Tridge, Just my take on this,
From what I have learned:
Some of the broadcast base station coordinates do not exactly match published values.
Also accuracy and time to fix is a factor of baseline distance. Accuracy of 1CM + 3ppm means that every 1KM in baseline you add 3mm of error to your accuracy.
Time to fix for multi band GNSS is about 10 seconds + 2 seconds per KM. Not such a big deal but still a factor.
All that said I have always had a base station at my disposal.

I look forward to the article and learning more…

(Hugues) #12

Fully agree. I tested the simplertk2b here (it is priced under 200 eur):

1 Like
(ZED-PV ) #13

If anyone is interested in a cheaper alternative to the ones mentioned above, have a look at this:

https://www.polaris-gnss.com/

I have no affiliation to them I have just used their products and I am happy with them so far.

I’m thinking of building a fixed wing UAV with this RTK system if it’ll be reliable enough in flight.

It is cheaper than all mentioned above.

If someone wants to test out the accuracy of the system I would be happy to help with setup / troubleshooting. I would also be happy to see the findings. : )

(Kikislater) #14

@ZED-PV it’s single frequency, here it’s totally different, f9p is dual frequencies : it allows longer baseline, faster fix. Your device looks like an m8t available in emlid reach rs+ or reach m+ … Good product but now it’s evolving !

1 Like
(ZED-PV ) #15

@kikislater Yeah it is sadly. It works pretty well for what it is and how it’s priced.

How much does single vs dual frequency affect baseline length? Accuracy wise?

It has a SkyTraq RTK chip in it not a ublox. I can’t find exactly which one right now.

(curt carroll) #16

The baseline length error is about the same it’s spec at 1cm + 1ppm. So that is 1 cm plus 1 mm per KM. 2CM & 3ppm is more realistic… L2 helps get a quick fix about 60x faster than L1 alone, still the best fix is usually L1. L2 just helps it calculate faster, same with other bands. L1 fix is generally the best.

(ZED-PV ) #17

@mtnsurveyor

Ah okay, just a more diverse and reliable fix then. The more the merrier.

Do you use any RTK capable commercial drones to do any survey work? Or custom built ardupilot bases ones?

Thanks Mountain Surveyor.

(curt carroll) #18

I have used only custom drones for surveying. All the complete commercial packages are out of my price range. I have made a few thousand dollars this year and $100 all years prior.
Until recently it has not been worth more than a hobby.

1 Like
(ZED-PV ) #19

@mtnsurveyor Aha okay, there’s more and more options on the market for much less than before.
If your custom rigs are doing their job then theres really no need for a commercial rig.

I will contact you once I start integration of RTK into my build if that’s fine with you?

Thanks For the chat.

(Kikislater) #20

Multi frequency have better Z accuracy however it adds some noise in phase so most of commercial multi frequency GPS unit switch from multi to single frequency if baseline is inferior to 10km

1 Like